Apparatus for the treatment of slurries of chemical reagents



Feb. 18, 1958 E. RQBURLING ETAL 2,823,986 APPARATUSFOR THE TREATMENT OF,SLURRIES OF CHEMICAL REAGENTS Filed Oct. 19, 1951 1 M, Y i FX, 55 Mm m7 r. v0! M BE J i i B N 1 United States Patent APPARATUS FOR THETREATMENT OF SLURRIES OF CHEMICAL REAGENTS Elmer R. Burling and John P.Rich, Nashua, N. H. Application October 19, 1951, Serial No. 252,122 4Claims. (Cl. 23260) It is an object of this invention to provide amethod and apparatus for carrying out large scale chemical reactionswhere the reagent is either corrosive, explosive or both. Specificallythis has reference to bleaching wood pulp with chlorine dioxide as setforth in our copending application Serial No. 252,121, filed of evendate herewith and now Patent No. 2,706,673, dated April 19, 1955.

It is a further object of this invention to provide a method andapparatus as aforesaid in which a minimum portion of the apparatus isbrought in contact with the reagent.

It is a further object of this invention to provide a method andapparatus as aforesaid in which migration of the reagent in activecondition beyond predetermined limits is absolutely prevented.

The above and other objects will be made clear from the followingdetailed description taken in connection with the annexed drawings inwhich:

Fig. 1 is a front elevation of the improved apparatus partly in section;and

Fig. 2 is a side elevation also partly in section.

The essential elements of the apparatus are a compacting tower 12, athick stock pump 14, a particularly designed line 16 connecting thestock pump with a mixer 18. Stock leaves the mixer 18 through a line 20to the base of a primary reacting tower 22. At the top of the primaryreaction tower 22 a line 26 connects it to a secondary reacting tower28. The base of the secondary reacting tower 28 has formed therein acone 32. A pair of agitating impellers 34 are provided b tween the coneand the inner wall of the tower 28. A number of inlet pipes 36 arebrought through the wall of the tower 28 adjacent the apex of the conewhile a pump 38 serves continuously to remove dilute stock from thebottom of the tower 28.

As illustrated pulp is delivered to the compacting tower 12 by a stockthickener but the thick stock might be obtained from any other source.

The line 16 between the pump 14 and the mixer 18 is calculated as tolength and diameter so that stock moving through it will form a plugseal against any migration of reagent backward from the mixer. The inletpipes 36 in the tower 28 serve not only to dilute the stock for handlingby the pump 38 but also to supply a neutralizing agent which willthoroughly overcome any corrosive or explosive efiect of any residualreagent. Accordingly only the mixer 18, the primary reaction tower 22,the line 26 and the secondary re action tower 28 need to be protectedfrom corrosion.

Gases may be bled from the top or" the tower 28 through a valve 40 andpreferably are conducted to a cooler or condenser 42 where vapor andcorrosive gases are condensed and the gases are redissolved so that thesolution thus obtained may be returned to the system and the venting ofcorrosive gases avoided.

For purposes of heating and dilution steam may be 2,823,986 PatentedFeb. 18, 1958 added to the stock in the compacting column 12 or to themixer 18 or both. In the case of certain types of very sensitivereagents it is desirable to have the stock very uniformly heated inwhich case it will be best to do the heating in the compacting tower 12.As an alternative, steam may be added to the primary reaction tower 22at a level where a sufiicien't amount of the reagent has been consumed.

It will be seen that due to the height of the primary reacting tower 22and the friction of stock flowing through this column the stock in themixer is under a very substantial pressure. This is especially desirablewhen the reagent such, for example, as chlorine dioxide is volatile oronly slightly soluble at atmospheric pressure. Actually the pressuregradually decreases as stock moves up through the tower 22. Then in thetower 28, once the tower is full, incoming stock moving downwardly issubjected to gradually increasing pressure.

All of the towers and the line 26 have unobstructed interiors so thatrelatively high density stock can pass through. In general thecross-sectional area of the tower 28 will be from 10 to 20 times that ofthe primary tower 22. This means that the reaction time in the tower 28has the same ratio to the reaction time in the tower 22. In many casesthe reaction will be percent complete by the time the stock leaves theline 26. The vastly greater reaction time in the tower 28 will usuallybe ample substantially to exhaust the reagent.

We claim:

1. Apparatus for reacting a high density aqueous slurry of wood pulpwith a volatile, corrosive reagent such as chlorine dioxide comprising:a thick stock pump for advancing a high density slurry; a mixer; aconduit connecting said pump to said mixer, said conduit beingproportioned with reference to the delivery of said pump so as to form agas tight plug of stock between the pump and the mixer; means forsupplying a solution of volatile, corrosive reagent to said mixer; aprimary vertical reaction tower receiving, at its base, a mixture ofsaid slurry and said reagent from said mixer; a secondary verticalreaction tower; a conduit connecting the tops of the two towers wherebyto deliver said slurry mixture from the primary tower to the secondarytower; said secondary tower .having adjacent its base a plurality ofnozzles for diluting the slurry mixture and an outlet for removing allof the dilute slurry mixture from the system at the base of thesecondary tower.

2. Apparatus as set forth in claim 1 in which the secondary tower has avolume from 10 to 20 times the volume of the primary tower.

3. Apparatus as set forth in claim 1 in which both towers haveuninterrupted cross section.

4. Apparatus as set forth in claim 3 in which the secondary tower has avolume from 10 to 20 times the volume of the primary tower.

References Cited in the file of this patent UNITED STATES PATENTS623,893 Fairley Apr. 25, 1899 1,330,136 Partington Feb. 10, 19201,459,777 Leiser June 26, 1923 1,576,705 Babcock Mar. 16, 1926 1,662,070Lyford Mar. 13, 1928 2,051,029 Curtis Aug. 18, 1936 2,055,836 CowlesSept. 29, 1936 2,332,527 Pyzel Oct. 26, 1943 2,494,588 Skooglund Jan.17, 1950 2,503,788 White Apr. 11, 1950 2,581,519 Critchley Ian. 8, 1952

1. APPARATUS FOR REACTING A HIGH DENSITY AQUEOUS SLURRY OF WOOD PULPWITH A VOLATILE, CORROSIVE REAGENT SUCH AS CHLORINE DIOXIDE COMPRISING:A THICK STOCK PUMP FOR ADVANCING A HIGH DENSITY SLURRY, A MIXER, ACONDUIT CONNECTING SAID PUMP TO SAID MIXER, SAID CONDUIT BEINGPROPORTIONED WITH REFERENCE TO THE DELIVERY OF SAID PUMP SO AS TO FORM AGAS TIGHT PLUG OF STOCK BETWEEN THE PUMP AND THE MIXER, MEANS FORSUPPLYING A SOLUTION OF VOLATILE, CORROSIVE REAGENT TO SAID MIXER, APRIMARY VERTICAL REACTION TOWER RECEIVING, AT ITS BASE, A MIXTURE OFSAID SLURRY AND SAID REAGENT FROM SAID MIXER, A SECONDARY VERTICALREACTION TOWER, A CONDUIT CONNECTING THE TOPS OF THE TWO TOWERS WHEREBYTO DELIVER SAID SLURRY MIXTURE FROM THE PRIMARY TOWER TO THE SECONDARYTOWER, SAID SECONDARY TOWER HAVING ADJACENT ITS BASE A PLURALITY OFNOZZLES FOR DILUTING THE SLURRY MIXTURE AND AN OUTLET FOR REMOVING ALLOF THE DILUTE SLURRY MIXTURE FROM THE SYSTEM AT THE BASE OF THESECONDARY TOWER.